1. Field of the Invention
The present invention relates to a semiconductor device, more particularly to an improvement in a container for housing a high-frequency semiconductor circuit using a radio-frequency wave such as a microwave or a millimeter wave.
2. Description of the Related Art
A conventional semiconductor device with a microwave circuit housed within a ceramic container suffers from degradation of circuit characteristics due to the frequency resonance of the container and from damage of the container due to the difference of the thermal expansion coefficient of the ceramic and the metal base plate.
To solve the problems of the conventional semiconductor device, an improved semiconductor device is disclosed in U.S. Pat. No. 571,542, wherein the container is substantially made of metal, with just the lead penetration portions for connection with the inner circuit made of ceramic.
However, with this structure, radio waves propagate from the input side to the output side within the container space, which causes undesired characteristics, e.g. noise on the output signal. This is because the impedance of a part of the circuit matches the impedance of the space within the container, which impedance is usually very high. This causes radiation of the microwave from the input side within the container, resulting in so-called rectangular waveguide mode signal propagation within the container. Therefore, the undesirable wave propagation occurs at a frequency which is used in the circuit of the container.
In order to avoid this, the cutoff frequency of the waveguide within the container must be higher than the frequency of the signal used in the circuit, since the waveguide functions as a high-pass filter. That is, the length of the longer side of the cross-section of the container inner space must be shortened according to the frequency of the signal.
The container requires supplementary space for handling parts of the microwave circuit in addition to and adjacent to the space for mounting the microwave circuit on the container bottom surface. Also, supplementary space is necessary for mounting parts of, for instance, a DC bias circuit of the microcircuit. If the inner length of the container is shortened with the intention of eliminating the above problem, the supplementary space of the container becomes insufficient.